Design and Use of Drogues

  • 04 Mar 2018 11:52
    Reply # 5888112 on 833331
    Anonymous member (Administrator)

    Annie,

    my experience is that the wind strength appears to be over-reported by boats around me. When I have sailed in something I estimate as a stiff breeze, other have told me that they recorded 30-35kts winds (F7-F8). I think the reason is that they have their wind sensor up in the mast top, some 12-15m up. I wonder what height is the standard height used by the met office? On the airports I worked on, the wind sensors seemed to sit on a standard mast, some 6-8m above the ground. I used to maintain them.

    In another posting, recently, you mentioned that you were not sure that a long keel was better offshore than a short keel. I am partly with you there. My Viggen, Malena was a brilliant seaboat, and very easy to control downwind.

    What I like with the quite long keel of my present IF, Ingeborg, is that I can deliberately slow her down to ease discomforts, when working against strong winds and sea. Thanks to her big keel area and slim lines, she will still not make much leeway. My fin-keeled Malena, on the other hand, had to be driven hard to windward, to keep her from going sideways as fast as forwards.

    The ideal keel shape for a cruiser would in my eyes be a longish finkeel with a flat sole and generous keel area, and then with one or two big, balanced rudders, right at the stern. The long keel would let it dry out without ever tipping on the nose, held upright only by a pair of legs. Even with twin keels, I would have them long and medium deep.

    I am looking forward to doing a towing test of my battery of home-made parachute drogues, and also of 2-3- ball fenders (20, 40 and 50cm). I hope the ball fenders will be useful in keeping a boat (which may be prone to ‘taking off’) from exceeding 7-8 kts, and still keep a decent progress.

    Cheers, Arne

    (Finally red numbers on the thermometer her, after staying for a while in the blues sector).


  • 03 Mar 2018 23:19
    Reply # 5887770 on 5885911
    Arne Kverneland wrote:

    What was the argument in the first place for designing the JSD? I can't help feeling that a not too complicated problem has ben solved in a maximum complicated way. People often get impressed by complicated designs, and mis-interpret them as 'good' or 'high quality'. The JSD appears to me to be quite awkward both to store and to handle.  

    BTW, the drag of any object towed through the air or water, rises not with the speed, but with the square of the speed.

    Arne

    I agree with you, Arne.  Admittedly, modern boats are very different animals from those that were common 50 years ago, but for all that, thousands of boats have successfully crossed oceans and survived gales without the help of a JSD.

    Two things worry me about these JSDs. 

    The first is that I have never met anyone who used one in earnest who didn't have a sorry mess at the end of it.  Even the ones built to spec seem to self-destruct to a certain extent.  In most cases, this won't really matter, because you should have time to rebuild the thing before the next severe weather hits.  But unless you are sailing somewhere where you are likely to end up in really severe weather, do you need such a device?  We sailed 110,000 miles in Badger and never dragged anything behind us and we didn't stick strictly to the Trade Wind route.

    The other thing that concerns me about them is that while they are not that difficult to deploy, they are a bit of a nightmare to retrieve.  In my experience, the worst of the waves come at you as the wind starts to take off, so that they start to lose their stability and topple all over the place.  This is when you get slammed by a wall of water that tries to knock the boat off her feet.  The best thing you can do is get her moving again so that she's no longer a sitting duck, but we might still be talking about winds of F8 where it's going to be both very difficult and potentially dangerous to haul the drogue in.

    Another thing that makes these discussions terribly difficult is that either I hopelessly underestimate wind strengths or everyone else overestimates them.  I can't tell you how many people I have met in recent years, who tell me that they have sailed to windward in 50 knots of wind with their jib partially rolled up and 2 reefs in the main, or carried sail in 55 knots.  I'm sorry, but their boats don't look so substantial that this would have been possible.  I don't believe that in over 40 years of sailing, I have ever been offshore in sustained winds of F10 (thank god), which is 48-55 knots and don't think I have been exceptionally lucky.  Hardly anyone uses the Beaufort scale these days (which has very good descriptions of sea state) and nearly everyone has instruments, which are showing the reading from a wildly gyrating recorder, 50+ feet in the air.  How accurate are these readings, I wonder?  I have seen weekend sailors turn away with a smirk from a dyed-in-the-wool ocean voyager, who stated that in his couple of hundred thousand miles of sailing, he had never encountered sustained winds of over 50 knots.  You could see them thinking that obviously he had never sailed in their back yard where such winds are common.

    I understand why people worry about heavy weather (I'm terrified of it, until I get to trust a boat), but really, I do think we tend to dwell on it too much.  As the Fastnet race of 1979 showed so clearly, it's generally the people who let the boats down, not the other way round.
  • 02 Mar 2018 23:44
    Reply # 5886047 on 833331

    I agree with David Tyler that the cones of JSD are likely to be unevenly loaded, and that many JSD devices have cones that are too lightly built.  Including mine.  I paid $1500 to a company in Australia that supplies the drogues and was shocked to discover how lightly built each cone was.  The material is super light and the single row of stitching on the inadequate tabling at each end of the cone is a joke.  I should have built my own cones and if I am ever going offshore again (unlikely) I will either restitch or replace the cones.  At least the warp they supplied is good!  I also carry a canvas Seabrake device from Burke that is superbly made.  I once had three of these, with the idea that I might put them in line, about 20m apart, and make my own version of the JSD, but some wretch stole two of them.  I think David's idea of 10 larger, very robust cones on the same length of line as the JSD is a brilliant idea.

    It might also be an idea to have two drag devices, one a JSD type and one standard drogue, as sometimes you want to stop altogether (or as much as possible), either because of dangers to leeward or really severe weather, and sometimes, in more moderate gales going your way, you are happy to run on at reduced speed.  A friend of mine used a Seabrake in the Southern Ocean and found it made steering the boat downwind in boisterous conditions much easier.  That was a big boat though.  A Seabrake would almost stop Arion in all but the fiercest weather, so for controlled running I'd need something with less drag.   The idea of towing a ball fender intrigues me.

    The wealth of experience and knowledge in these fora is a real treasure.

  • 02 Mar 2018 22:07
    Reply # 5885911 on 833331
    Anonymous member (Administrator)

    What was the argument in the first place for designing the JSD? I can't help feeling that a not too complicated problem has ben solved in a maximum complicated way. People often get impressed by complicated designs, and mis-interpret them as 'good' or 'high quality'. The JSD appears to me to be quite awkward both to store and to handle.  

    BTW, the drag of any object towed through the air or water, rises not with the speed, but with the square of the speed.

    Arne

    Last modified: 02 Mar 2018 22:07 | Anonymous member (Administrator)
  • 02 Mar 2018 20:57
    Reply # 5885768 on 5885485
    Scott Dufour wrote:

    A year or so ago, Practical Sailor ran reviews of small drogues designed slow a boat, but give it enough speed to steer into a harbor.  I wrote to ask about using an undersized Jordan Series to perform this function - and their response was excellent - the forces on any given cone is proportional to its speed through the water.  A Jordan series drogue is designed to pretty much stop a boat completely relative to the water.  So each cone moves very little, and consequently takes little force.  If there weren't enough cones let out, though, then the boat would be moving, and the cones taking more load than they could handle.  Ineffective mess ensues.  Better stick to something designed for the drag-but-let-run-a-bit.

    Where that falls down is the assumption that when fully deployed, all JSD cones are equally loaded. I don't believe that to be the case. In the circular motion of the water within a wavetrain, some cones are going to be unloaded or lightly loaded (at the top of the wave) and some are going to be more heavily loaded (at the bottom of the wave). So each cone has to be constructed on the assumption that it will carry more than its fair share of the load, quite frequently, and therefore, a lesser number of cones should be able to cope with the boat-slowing task without failing.

    Trevor Robertson's experience  (and he's not the only one) indicates to me that some (not all) JSDs have been made without sufficient attention to the weight of the material and the finishing of the cones, as so many of them failed. It's not too surprising, as there is a lot of labour in making a hundred or more cones. Mr Jordan was asked if it might not be just as good, and easier, to make a smaller number of cones, to a larger size so as to give the same effective area, and his reply was along the lines of: "if it ain't broke, don't fix it". I would be inclined towards using (say) ten big cones, more stoutly constructed, and spread out along the line so that the finished length of the drogue was the same as for a hundred cones, thus putting all the cones in different parts of the waves, and again, averaging out the pull exerted, moment by moment, on the boat. But since my ocean-cruising days are over and done with, that's just a hypothesis I won't be testing.

  • 02 Mar 2018 18:29
    Reply # 5885485 on 833331

    There are three different uses of drogues we're talking about.  Stopping a boat in heavy seas and weather, slowing a boat for more steering control in heavy weather, and slowing a boat for momentary deck fiddlin'.

    The Jordan series drogue is for stopping a the boat in heavy weather, hunkering down, and surviving.  The Jordan series drogue's major benefit is that in heavy weather, it doesn't pull out of the wave face like a parachute (or I daresay, a floaty fender) does.  In heavy seas tactics, parachute drogue advice is to "match the wave train pattern, three waves back."  Not so easy to do.  The Jordan Series, with its tiny cones along hundreds of feet, allow for a more elastic, low shock load, response to varying wave trains, and any particular cone pulling out of the wave face has little overall effect.

    A year or so ago, Practical Sailor ran reviews of small drogues designed slow a boat, but give it enough speed to steer into a harbor.  I wrote to ask about using an undersized Jordan Series to perform this function - and their response was excellent - the forces on any given cone is proportional to its speed through the water.  A Jordan series drogue is designed to pretty much stop a boat completely relative to the water.  So each cone moves very little, and consequently takes little force.  If there weren't enough cones let out, though, then the boat would be moving, and the cones taking more load than they could handle.  Ineffective mess ensues.  Better stick to something designed for the drag-but-let-run-a-bit.

    For just slowing the boat for momentary fiddling, I bet any of the above would work - a bit of Jordan series, a little parachute, or a round fender experiencing downward lift from movement over water.

    Last modified: 02 Mar 2018 18:31 | Anonymous member
  • 02 Mar 2018 12:38
    Reply # 5884928 on 5884830
    Storm management can—and does—get complicated fast."
    I am reminded of Blackshaw in his book Mountaineering discussing the descent of a steep snow slope by sliding or glissading.  Quoted from memory:  

    "There are three positions of the glissade, the standing, the sitting and the involuntary - and they usually follow one another in quick succession."  

  • 02 Mar 2018 09:50
    Reply # 5884830 on 5883282
    Martin Gronow wrote:

    Hi, 


    I know absolutely nothing of heavy weather sailing but this chap has circumnavigated 3 times....and loves towing stuff...including fenders...here


    Also check out what happens to a JSD after a couple of (albeit) heavy uses...here



    Regards

    Martin

    From the sales pitch for Goodlander's book on Amazon:

    "Heavy weather management is simple—there are only two basic rules. The prudent mariner must control his vessel’s speed and angle to the wind and seas. That’s it. There’s nothing complicated about these concepts. However, the offshore execution of these concepts at sea in 50+ knots of breeze and 30+ foot seas—what we traditionalists call offshore seamanship—can vary greatly depending on the boat type, number of hulls, sea state, wind force, the proximity and direction of land, the presence of ocean currents, underwater topography, and a hundred other evolving factors. Storm management can—and does—get complicated fast."

    Puts it better than I can.

  • 02 Mar 2018 08:08
    Reply # 5884801 on 833331

    Hi, 


    I'm sure Capt Fatty wont mind me posting this from his book I referenced below...where most heavy weather authors tend to sit on the fence the Capt tells it like it it.


    Regards

    Martin


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  • 02 Mar 2018 06:32
    Reply # 5884775 on 5883398
    David Tyler wrote:

    Soooo, can we take this one stage further? Can we invent the "Arne Series Drogue"? Get six round fenders to serve their normal purpose, and when the need arises, tie them all onto a long line and tow them behind us?

    Fenders are very strong, but are they that strong?  Maybe you need each fender on its own line, spread out in a fan astern like Eskimo huskies?  Unfortunately, just like when the dogs decide to fight instead of pull, I see a great potential for a snarl up.
    Last modified: 02 Mar 2018 06:33 | Anonymous member
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